Whole blood consists essentially of red blood cells, white blood cells, platelets and plasma. These components are required for different therapeutic usage and therefore whole blood resulting from a donation is generally processed in order to extract them. This is done in two steps. A first step consists in collecting whole blood from a donor into a primary bag containing an anticoagulant solution. A typical blood donation lasts between 5-10 min., to collect a fixed volume generally of 450 ml of whole blood. This fixed volume excludes a certain range of the donor population due to risks of hypovolemia, as standard blood bank practices limit collection to 15% of the total blood volume of a donor. Once the collection is completed, the donor is released and the second step can be initiated. It consists in separating the blood into its sub-components through a batch process. This is done by spinning the blood bag for a period of about 10 minutes in a large refrigerated centrifuge. The main blood constituents, erythrocytes, platelets and white cells, plasma having sedimented and formed distinct layers, are then expressed sequentially by a manual extractor in different satellite bags attached to the primary bag.
More recently, automated extractors have been introduced in order to facilitate the manipulation. Nevertheless, the whole process remains laborious and requires the separation to occur within a certain time frame to guarantee the quality of the blood components. This complicates the logistics, especially considering that most blood donations are performed in decentralized locations where no batch processing capabilities exist.
This method has been practiced since the widespread use of the disposable plastic bags for collecting blood in the 1970's and has not evolved significantly since then. Some attempts have been made to apply haemapheresis technology in whole blood donation. This technique consists of drawing and extracting on line one or more blood components while a donation is performed, and returning the remaining constituents to the donor. However, the complexity and costs of haemapheresis systems preclude their use by transfusion centers for routine whole blood collection.
There have been various proposals for portable, disposable, centrifugal apparatus usually with collapsible bags, for example as in U.S. Pat. Nos. 3,737,096, or 4,303,193, or with a rigid walled bowl as in U.S. Pat. No. 4 889,524. These devices all have a minimum fixed holding volume which requires a minimum volume usually of about 250 ml to be processed before any components can be collected.
U.S. Pat. No. 5,316,540 discloses a centrifugal processing apparatus corresponding to the precharacterizing part of claim 1, wherein the processing chamber is a flexible processing bag which can be deformed to fill it with biological fluid or empty it by means of a membrane which forms part of the drive unit.
EP-A-0 654 669 discloses a centrifugal processing apparatus having two chambers separated by a piston. Before centrifugation, a small quantity of fluid to be processed is taken in via an off-center inlet, and is transferred between the two chambers during centrifugal processing.
There remains a widespread need for a system that, during blood collection, will automatically separate the different components of whole blood that are differentiable in density and size, with a simple, low cost, disposable unit.